The invention relates to a process for the reattachment of a thread in an open-end spinning machine having at least one spinning motor. For this purpose, a thread is introduced into the rotating spinning rotor where it attaches itself to a ring of fibers located in the fiber collection groove of the spinning rotor. Subsequently, the thread is drawn out of the spinning rotor and is wound up on a driven windup spindle. A pair of drawoff rollers is provided between the spinning rotor and the windup spindle. The invention further relates to an apparatus for carrying out this process.
When it is intended to attach, i.e., re-spin a thread, in an open-end spinning machine having spinning rotors, for example when a thread breakage has occurred, the end of the thread must be guided back from the spindle into the spinning rotor. There it is attached to the fiber ring located in the rotating spinning rotor. From the moment that the end of the thread combines with the fiber ring, the thread is twisted and can be continuously drawn off so that a new thread is continuously formed from fibers pulled out of the fiber collection groove. In known manner, the fibers are guided pneumatically and continuously to the fiber collection groove. It is important that, in each instance of a new re-spinning of a thread to the fibers located within the spinning rotor, the pullout of thread from the spinning rotor takes place at a point in time when the thread end combines with the fiber ring located in the spinning rotor, because otherwise, excessive twisting of the thread, i.e., imparting too many rotations per unit length, would break the thread and this would lead to a failure of the re-spinning process and a new re-spinning attempt would be required.
When the end of the thread fed into the spinning rotor for the purpose of re-spinning is dragged along and shares the rotation of the spinning rotor, it undergoes a sudden increase of tension and simultaneously, the end of the thread is twisted onto the fibers deposited in the fiber collection groove of the spinning rotor and the thread breakage is thereby relieved. According to the present invention, this increase of the tensile stress in the thread is used as a signal for beginning to draw the thread out of the spinning rotor.
It has been shown that the attachment, i.e., the re-spinning of threads onto spinning rotors which run at very high rpm, for example, at 60,000 rpm and higher, is very difficult. In such cases, if the drawoff of the thread does not begin immediately after the attachment, i.e., after twisting the thread onto the fiber ring, then the thread is twisted off and broken in a very short time and the re-spinning attempt must then be repeated. This can be easily understood if it is realized that when the rotor turns at 60,000 rpm, in only half a second it imparts 500 rotations to a stationary and already twisted piece of thread which has a length of only approximately 10 cm as between the fiber collection groove and the thread guiding members which prevent further twisting. This comes to approximately 5,000 twists per meter of thread length which would be sufficient to twist off and break even fine threads. On the other hand, if the thread is drawn off too early, i.e., before the end of the thread guided into the spinning rotor has been twisted onto the fiber ring located therein, the attachment process has effectively failed also.
The period of time which elapses between sensing the increase of the tensile force in the thread due to its sharing the rotation of the spinning rotor and the time when the thread is already twisted too much is too short for a purely manual re-spinning operation when rotor speeds of approximately 60,000 rpm are used, i.e., the time which is available to an operator for sensing the increase of the tensile force in a piece of thread guided into the rotor and for the initiation of the drawoff process of that thread is too short: the thread is twisted off and breaks before the operator can react to the increase of the tensile force and can initiate the drawoff of the thread. Therefore, until the present time, it has been necessary to reduce the operating speed of the machine when a thread was being reattached. However, this is cumbersome, requires a separate apparatus (German Offenlegungsschrift No. 2,314,473) and results in a reduction of the productive capacity of the machine.